The fineness of a precious metal object (coin, bar, jewelry, etc.) represents the weight of fine metal therein, in proportion to the total weight which includes alloyingbase metals and any impurities. Alloy metals are added to increase hardness and durability of coins and jewelry, alter colors, decrease the cost per weight, or avoid the cost of high-purity refinement. For example, copper is added to the precious metal silver to make a more durable alloy for use in coins, housewares and jewelry. Coin silver, which was used for making silver coins in the past, contains 90% silver and 10% copper, by mass. Sterling silver contains 92.5% silver and 7.5% of other metals, usually copper, by mass.
Various ways of expressing fineness have been used and two remain in common use: millesimal fineness expressed in units of parts per 1,000[1] and karatsorcarats used only for gold. Karats measure the parts per 24, so that 18 karat = 18⁄24 = 75% and 24 karat gold is considered 100% gold.[2]
Millesimal fineness is a system of denoting the purity of platinum, gold and silveralloysbyparts per thousand of pure metal by mass in the alloy. For example, an alloy containing 75% gold is denoted as "750". Many European countries use decimal hallmark stamps (i.e., "585", "750", etc.) rather than "14 k", "18 k", etc., which is used in the United Kingdom and United States.
It is an extension of the older karat system of denoting the purity of gold by fractions of 24, such as "18 karat" for an alloy with 75% (18 parts per 24) pure gold by mass.
The millesimal fineness is usually rounded to a three figure number, particularly where used as a hallmark, and the fineness may vary slightly from the traditional versions of purity.
Here are the most common millesimal finenesses used for precious metals and the most common terms associated with them.
999.999—six nines fine: The purest gold ever produced. Refined by the Perth Mint in 1957.[3][4]
999.99—five nines fine: The purest type of gold currently produced; the Royal Canadian Mint regularly produces commemorative coins in this fineness, including the world's largest, at 100 kg.[5]
900—one nine fine: American Eagle denominations for 1837–1933; currently used in Latin Monetary Union mintage (e.g. French and Swiss "Napoleon coin" 20 francs).
899—American Eagles briefly for 1834—1836.
834—20 karat
750—18 karat: In Spain oro de primera ley (first law gold).
625—15 karat
585—14 karat
583.3—14 karat: In Spain oro de segunda ley (second law gold).
500—12 karat
417—10 karat: Lowest legal solid gold karat made in the US prior to the August 2018 revision of the FTC Guides (Now 1 karat is legal).
375—9 karat: Minimum standard for gold in some of the Commonwealth realms: Australia, Canada, New Zealand, UK, etc. It is also the minimum in Austria, Ireland, Portugal and France.
333—8 karat: Minimum standard for gold in Germany after 1884.[6] It is also the minimum for Denmark, Greece and Mexico.
1 karat: Legal minimum for gold in the US since the revision of the FTC Guides of August 2018.
935: Swiss standard for watchcases after 1887, to meet the British Merchandise Marks Act and to be of equal grade to 925 sterling. Sometimes claimed to have arisen as a Swiss misunderstanding of the standard required for British sterling. Usually marked with three Swiss bears.
935: used in the Art Deco period in Austria and Germany. Scandinavian silver jewellers used 935 silver after the 2nd World War
925: (37⁄40) Sterling silver The UK has used this alloy from the early 12th century. Equivalent to plata de primera ley in Spain (first law silver)
917: a standard used for the minting of Indian silver (rupees), during the British raj and for some coins during the first Brazilian Republic.
875: 84 zolotnik is the most common fineness for Russian silver. Swiss standard, commonly used for export watchcases (also 800 and later 935).
868: 83 1⁄3 zolotnik. Imperial Russian coinage between 1797[10] and 1885.[11]
835: A standard predominantly used in Germany after 1884, and for some Dutch silver; and for the minting of coins in countries of the Latin Monetary Union
833: (5⁄6) a common standard for continental silver especially among the Dutch, Swedish, and Germans
830: A common standard used in older Scandinavian silver
800: The minimum standard for silver in Germany after 1884; the French 2nd standard for silver; "plata de segunda ley" in Spain (second law silver); Egyptian silver; Canadian silver circulating coinage from 1920-1966/7[12]
750: An uncommon silver standard found in older German, Swiss and Austro-Hungarian silver
720: Decoplata:[13] many Mexican and Dutch silver coins use this standard, as well as some coins from Portugal's former colonies,[14] Japan,[15] Uruguay,[16] Ecuador, Egypt, and Morocco.
500: Standard used for making British coinage 1920–1946 as well as Canadian coins from 1967-1968, and some coins from Colombia and Brazil.
400: Standard used for US half dollars between 1965 and 1970, and commemorative issue Eisenhower dollars between 1971 and 1978. Also used in some Swedish Krona coins.
The karat (US spelling, symbol korKt) or carat (UK spelling, symbol corCt)[17][18] is a fractional measure of purity for goldalloys, in parts fine per 24 parts whole. The karat system is a standard adopted by US federal law.[19]
24-karat gold is pure (while 100% purity is very difficult to attain, 24-karat as a designation is permitted in commerce for a minimum of 99.95% purity), 18-karat gold is 18 parts gold, 6 parts another metal (forming an alloy with 75% gold), 12-karat gold is 12 parts gold (12 parts another metal), and so forth.[20]
In England, the carat was divisible into four grains, and the grain was divisible into four quarts. For example, a gold alloy of 127⁄128 fineness (that is, 99.2% purity) could have been described as being 23-karat, 3-grain, 1-quart gold.
The karat fractional system is increasingly being complemented or superseded by the millesimal system, described above for bullion, though jewelry generally tends to still use the karat system.
Conversion between percentage of pure gold and karats:
However, this system of calculation gives only the mass of pure gold contained in an alloy. The term 18-karat gold means that the alloy's mass consists of 75% of gold and 25% of other metals. The quantity of gold by volume in a less-than-24-karat gold alloy differs according to the alloys used. For example, knowing that standard 18-karat yellow gold consists of 75% gold, 12.5% silver and the remaining 12.5% of copper (all by mass), the volume of pure gold in this alloy will be 60% since gold is much denser than the other metals used: 19.32 g/cm3 for gold, 10.49 g/cm3 for silver and 8.96 g/cm3 for copper.
Carob (Ceratonia siliqua) pod and seeds, origin of karat via Arabic qīrāṭ which itself comes from the Greek word for the seed kerátion
Karat is a variant of carat. First attested in English in the mid-15th century, the word carat came from Middle Frenchcarat, in turn derived either from Italian carato or Medieval Latin carratus. These were borrowed into Medieval Europe from the Arabicqīrāṭ meaning "fruit of the carob tree", also "weight of 5 grains", (قيراط) and was a unit of mass[21] though it was probably not used to measure gold in classical times.[22] The Arabic term ultimately originates from the Greekkerátion (κεράτιον) meaning carob seed (literally "small horn")[22][23][24] (diminutive of κέρας – kéras, "horn"[25]).
In 309 AD, Roman EmperorConstantine I began to mint a new gold coin solidus that was 1⁄72 of a libra (Roman pound) of gold[26] equal to a mass of 24 siliquae, where each siliqua (orcarat) was 1⁄1728 of a libra.[27] This is believed to be the origin of the value of the karat.[28]
While there are many methods of detecting fake precious metals, there are realistically only two options available for verifying the marked fineness of metal as being reasonably accurate: assaying the metal (which requires destroying it), or using X-ray fluorescence (XRF). XRF will measure only the outermost portion of the piece of metal and so may get misled by thick plating.
That becomes a concern because it would be possible for an unscrupulous refiner to produce precious metals bars that are slightly less pure than marked on the bar. A refiner doing $1 billion of business each year that marked .980 pure bars as .999 fine would make about an extra $20 million in profit. In the United States, the actual purity of gold articles must be no more than .003 less than the marked purity (e.g. .996 fine for gold marked .999 fine), and the actual purity of silver articles must be no more than .004 less than the marked purity.[29]
A piece of alloy metal containing a precious metal may also have the weight of its precious component referred to as its "fine weight". For example, 1 troy ounce of 18 karat gold (which is 75% gold) may be said to have a fine weight of 0.75 troy ounces.
Most modern government-issued bullion coins specify their fine weight. For example, the American Gold Eagle is embossed One Oz. Fine Gold and weighs 1.091 troy oz.
Fineness of silver in Britain was traditionally expressed as the mass of silver expressed in troy ounces and pennyweights (1⁄20 troy ounce) in one troy pound (12 troy ounces) of the resulting alloy. Britannia silver has a fineness of 11 ounces, 10 pennyweights, or about silver, whereas sterling silver has a fineness of 11 ounces, 2 pennyweights, or exactly silver.
^Thomas, Athol. 90 Golden Years, The story of the Perth Mint. Gold Corporation. p. 58.
^Royal Canadian Mint. "The Million Dollar Coin – a true milestone in minting". Archived from the original on 9 March 2015. Retrieved 13 July 2017. In October 2007, the Million Dollar Coin was certified by Guinness World Records to be the world's largest gold coin.
The dictionary definition of fineness at Wiktionary
